1. Field of the Invention
The present invention relates to a total organic carbon measurement apparatus for determining a total organic carbon (TOC) content in an aqueous sample, and more particularly to a total organic carbon measurement apparatus designed to separate organic substances contained in low-impurity water, called “pure water” or “ultra-pure water”, through a carbon-dioxide separation unit, and determine a TOC content of the water based on conductivity.
2. Description of the Related Art
With a view to water quality management, a sample of low-impurity water, such as pharmaceutical waters, semiconductor manufacturing process waters, cooling waters, boiler waters or drinking waters, is subjected to TOC measurement to measure organics contained therein.
There has been known a TOC measurement method which comprises the steps of: converting organic compounds in an aqueous sample to carbon dioxide by an oxidation reactor; passing the aqueous sample containing the carbon dioxide into a carbon-dioxide detection mechanism including a conductivity measurement device, through a gas permeable membrane selective for passage of carbon dioxide; and measuring a conductivity of the aqueous sample by the carbon-dioxide detection mechanism [see JP 2510368B or corresponding U.S. Pat. No. 5,443,991].
In the TOC measurement method, a technique of measuring a conductivity of a carbon dioxide-containing aqueous sample includes arranging at least two electrodes at respective positions before and after oxidation of organic compounds in an aqueous sample, to detect a difference between conductivities before and after the oxidation (see JP 2001-281189A).
One such example is A-1000 TOC analyzers produced by Anatel Corporation.
There has also been known a technique of providing a carbon-dioxide separation unit adapted to transfer only carbon dioxide from an aqueous sample to measurement water, measuring a conductivity of the measurement water containing the carbon dioxide, and determining a TOC content of the aqueous sample according to calculation based on the measured conductivity, to reduce the influence of ionic impurities so as to provide a relatively small TOC measurement apparatus with enhanced measurement accuracy. One such example is Sievers® Series TOC Analyzers produced by GE Analytical Instruments.
In the configurations of the above apparatuses, it is necessary to provide flow passages for the aqueous sample and the measurement water, and therefore various pipes made of different materials have to be used for connecting the organics oxidation unit, the carbon-dioxide transfer/separation unit and the conductivity measurement unit. Thus, these apparatuses are likely to be affected by contamination due to elution of the pipe materials or the like.
Moreover, in these apparatuses, each component is apt to become larger in size, which leads to an increase in consumption of the aqueous sample and the measurement water. Thus, it is required to take measures to reduce the consumption of the aqueous sample and the measurement water, such as addition of an acid for facilitating transfer of dissolved carbon dioxide and/or an oxide (e.g., potassium peroxodisulfate) for ensuring decomposition of organics.
Although microfabrication techniques may be utilized to facilitate reduction in size of the apparatus so as to reduce the consumption of the aqueous sample and the measurement water, a flow rate thereof will be undesirably lowered.
Specifically, if the TOC measurement apparatus is downsized using microfabrication techniques to reduce the consumption of the sample and the reagents, the influence of eluates from the pipe materials and/or carbon dioxide to be transferred will become more prominent along with a resulting decrease in flow rate of the liquid.